Calcium sulphate pigment and method for preparing the same



Patented Feb. 15, 1944 UNITED STATES PATENT OFFICE CALCIUM SULPHATE PIGMENT AND METHOD FOR PREPARING THE SAME Franklin L. Kingsbury, Rumson, and Frank J. Schultz, Fords, N. J., assignors to National Lead Company, New'ycrk, N. Y., a corporation of New Jersey No Drawing. Application March 15, 1941,

Serial No. 383,548

8 Claims.

calcium sulphate, for instance, composite titanium dioxide-calcium sulphate pigment.

The bodying properties of. a pigment may be defined as the tendency of a. pigment to influence the consistency of film-forming surface coating compositions. This property of a pig ment, particularly calcium sulphate pigments, such as titanium dioxide-calcium sulphate pigment. is usually developed through the use of so-called "bodying agents which are added to pigmented film-forming compositions particularly flat wall paints for thepurpose'of increasing the consistency of the composition. Bodying agents most commonly used are water and soap solutions. in .consistency, developed by the bodying agent will vary depending upon the nature of the pigment portion of the film-forming material, and it has been found inconnection with titanium dioxide-calcium sulphat pigments that different batches although containing the same relative proportions of titanium dioxide and calcium sulphate give different bodying effects when incorporated in film-forming vehicles to which a bodying agent is added.

' It will be appreciated that the control of the bodying properties of calcium sulphate pigments presented aproblem of, considerable importance to the industry. The present invention provides a simple and effective solution ofthat problem.

A proper understanding of the invention necessitates a brief consideration of what is meant by the term consistency as applied to a film'- forming composition, e. g., a paint, and the method of determining it. The consistency of, for instance, a paint has been defined as its resistance todeformation or flow which resistance may be due to viscosity or to plasticity. The method of determining consistency which was employed to obtain the results hereinafter re- P rted was as follows:

An instrument sometimes called a consistom- The extent of bodying, i. e. increase ported by' the base for guiding the fall of the plunger. The cylinder is provided with a mark on its inner surfaces to fix the level to which it is to be filled with paint. The plunger rod has two marks 5 cm. apart which determine the distance of the plungers fall through the paint. The disc is perforated with 25 holes about I16 inch in diameter.

The procedure for testing the pigment involved Weighing grams of thepigment into a porcev lain enamel cup. A sufficient amount of filmforming vehicle was added to form a paste suitable for grinding when the pigment-vehicle mixture is worked together. The paste was weighed in order to ascertain the weight of vehicle used.- It was then run once through a three-roll laboratory mill and after this treatment cut down with additional vehicle so that the paint contains 56 per cent pigment and 44 per cent vehicle. (The vehicle was a processed tung-linseed oil mixture-containing 30 per cent of vola- 100 grams of th paint so pre- I tile thinner). pared were weighed into a suitable vessel and 0.5 cc. of a 2.0 per cent cobalt naphthenate drier added thereto.

The bodying ofa paint prepared as above described was effected by adding tothe 100 gram sample 1.5 cc. of a soap solution after the drier had been incorporated. The soap solution was mixed in by stirring, for instance, using a low speed iorkedstirrer turning at 750 R. P. M., for

exactly 6 minutes. After stirring, the paint was allowed to stand to permit the escape of entrapped air and to allow the body to develop which requires a minimum of one-half hour. (The soap solution was prepared by dissolving 1 part by weight of a neutral soap, e. g. Ivory soap flakes, in 99 parts of distilled water and adding thereto parts by weight of ethyl alcohol.) In determining the bodying characteristics of a pigment, determinations were made both on the paint containing no soap solution as well as on the paint sotreated.

In carrying out the test in the mobilometer the paint was poured into the cylinder up to r the inner mark. The plunger was fastened in of the paint.

eter or "mobilometer was employed. This instrument consists of a base plate provided with adjustable screw legs for leveling the instrument, a tall cylinder supported by the base plate'for receiving he paint to be tested, a plungerhaving a perforated disc at one end and a weight 1 pan at the other, and a guide bracket also supthe guide bracket while holding it above the level The weighting pan and suflicient additional weight so that the Weight of the plungerplus pan plus added weight equals a predetermined value was placed on the plunger and the perforated disc immersed in the paint to a depth so that the lower mark on the stem of the plunger was just visible above the collar of'the guide bracket. -The plunger was held in this position for exactly 30 seconds. The plunger was then allowed to fall through the paint, the time required for he upper mark on the plunger stem to reach the collar of the guide bracket being taken by a stop watch. (The weight the plunger plus pan plus added weight for test ing paints containing no. bodying agent was 20 grams: that for bodied paints 40 grams or, if necessary, because of the heavy body 75 grams or even 125 grams.) I

The above test was carried out at 70 and a relative humidity of 50%.

The results obtained were expressed as gramseconds which is the product of multiplying the ing tendency desired. Amounts between about 0.05 per cent and about 2.0% cover for all practical purposes the two extremes. Ordinarily, amounts of treating agent ranging from about 0.1'pe r cent to about 1.0 per cent are efiective, a preferred range being from about 0.1 per cent to about 0.5 per cent, calculated on the weight of the pigment.

The amino-compound may be admixed with pigment particles in any convenient manner. If

the amine is a solid it may be incorporated with the dry finished pigment by intimate mixing means. If the amine is a liquid, or if a solution of solid amine is employed, it may be sprayed weight of the plunger plus pan plus added weight upon the y pi m nt n if n ss ry th by the time in seconds required for the plunger solvent may be removed by evaporation. If the to fall the distance between the two marks, i. e.-, amine is to be add d t a pi m nt which in the 5 cm. (For a complete discussion of consistency course of manufacture is subjected to a milling of paints and methods and apparatus for evaltreatment, ei her wet or dry millin 1 b h, the uating consistency the reader is referred to chapaddition may be made prior to, during, or after ter 17, page 561 et seq. Physical and Chemical such milling treatment. Ifthe pigmentrequires Examination of Paints, varnishes, Lacquers and a calcination treatment the amine should-always Colors,by Dr. Henry A. Gardner, eighth edibe added after such treatment. Inshort the tion, 1937, distributed by the Institute of Paint method, of in rp ration is n t in itself. of. parand Varnish Research, Washington, D. C.) ticular importance provided an intimate associa: From the, foregoing it will be appreciated that tion of amino-compound and pigment'particles-is. a pigment having undesirable bodying character- I achieved. I i 1-; istics will exert a detrimental effect on the fln- I Having generally described the in'ventlomthe I ished surface coating compositions containing it. following examples will. more specifically. il1us- Very often it is found that the undesirable bodyirate itI ing characteristic is in the nature of a tendency EXAMPLE I I I toward excessive bodying and-there is need or I some means of lowering the bodying tendency. 4 2 FPaP u g The consistency of the paint obtained after the Y ,if p ate n F of 30 per F addition of the bodying agent, usually water or a and 70 P cent was w soap, solution is known as. bodied consistency}? aqueous 93 of ie e fie e that 'of the untreated paint as funbodied con Nm(CI-I ;CH NH) CH ,CH NH I I I sisten vifl I a and then tumbled and dried at 120 c to 150 -0 Thus, is an object of thepresent invention I T I v to pr means for lowering the beam tendq to evaporate the water. The amount of treating agent added was calculated to be'0.2 6 per cent? based on the weight of the pigment. The treated I and dried product was then pulverizedcinf'a'. :Rsymond mill, a r separated and then passedthroug a. hammer'mill tofurther'insure an even distribution, of the amine.v a.

ency of calcium sulphate pigments. It is another object of the present invention to provide means for treating pigmentary .calcium sulphate and composite titanium dioxide-calcium sulphate pigments' so that paints may be prepared fromsuch treated Pig ents possessing any predetermined consistency. These and other objects of the invention will become apparent-from the present de cr n; i i mixin dis sibilit yin'g' 1 i broadest asp the invention Q1 iil bility and ss .whzn i i iz i gra t ed t;t t1Z$c-* plates determining the-bodying tendency or-a. 5 m

' calcium sulphate pigment by-testing a sample of,

thefpigment'and if it be, desired to lower the bodying tendency to admix with the pigment a small amount of anorganic aliphatic amine. I

Thus, according to the invention, it has been found that the addition of small amounts of ethylene amines, such as ethylene diamine, so thb: modified Gardner 'mob ilometer'referredto t f pm- ExA'it rm II- d'eth lene riam e. l

l y I To a dry. m lled composite :titaniumgdioxid -c calcium phate pigment; obtained by co-precipiz' I triethylene tetramine,

undcmcmnncm.cmuncnscnamn etc., as well as aliphatic alcohol amines, such as isopropanol amine, CH2.CHOH.CH.NH2, triethan- 7 olamine, N (CzHtOH) 3, etc., will lower the bodying tendency of calcium sulphate pigments.

The amount of amino-compound to be admixed a with the calcium sulphate pigment will vary depending upon the amount of lowering in bodywereabodied by r the "addition of a This pigment treated according' toour new:

process was superior to a similarly" milled and disintegrated untreated pigment in.- respect when the coating compositions prepared with, the treated andtheuntreated'c'omposite pigment small amount of water it was found that our novel water se sitivity reducing-treatment had lowered the con? sistency of the paint about 50 per by the results obtained from tests cent-{as shown" tation, 30 per cent-TiOa-TO percent 011804, was Y added at auniform ratein a screw conveyor as the pigment was being fed to 0.2 per cent diethylene triamine,

' unacnacinuncnicmnm carried'out a hammer mill,

ing, color stability, gloss and gloss retention when incorporated into organic coating vehicles.

When a small amount of bodying agent (water) a was added to a fiat wall paint formulated-with treated and 'untreatedpigment, .1 it was found .,,that, because Q educed water sensitivity brought about by our novel treatment, the viscosityxor consistency of the paint was reduced about '10 perc nt.

After longstorage in cans it was found that the untreated pigment had settled out to a hard cake which could be redispersed in the vehicle only with great dimculty. The paint prepared with the amino-treated pigment, however, had settled to a soft, easily redispersible cake.

EXAMPLE III A composite titanium dioxide-calcium sulphate pigment, 30 per cent TiOz-ZO per cent C8504, obtained by wet mixing prior to recalcination, was milled in an edge runner mill with 0.4 per cent tetraethylene pentamine,

nnncmcnerimacnecnmne based on the weight of the pigment followed by gloss characteristics.

When a small amount of bodying agent (water) was added to fiat wall paints formulated with the untreated pigment and with pigment treated with tetraethylene pentamine according to this example, it was found that the viscosity as dey termined in the modified Gardner mobilometer was reduced about 70 per cent. The amine treated pigment also showed superior settling characteristics on long storage of paints formulated therewith.

EXAMPLE IV A calcium sulphate, prepared by running a lime slurry into excess concentrated sulphuric acid followed by steaming until the hydrated portion of the calcium sulphate was completely converted to the anhydrous form, was 'deliquored, washed and dried and then calcined at about 700 -C.

This calcium sulphate anhydrite was mixed with unmilled T: in the proportion 30 parts TiOa to 70 parts C8504 and then mixed with 0.5% of mixed isopropanolamines, then milled in an edge runner mill and passed through a hammer mill. The same mixture without the amine treatment was similarly milled and disintegrated.

The treated and the untreated pigments were then used in the formulation of flat wall paints whereto, for the purpose of increasing the consistency a small amount of bodying agent, water, was added.

It was found that the paint formulated with the untreated pigment became so viscous that it could not be applied with the brush. The paint formulated with the amine treated pigment according to our process however developed a desirable consistency. Other properties such as dispersibility, dryi color stability of the dried film and gloss characteristics, as well as settling characteristics also were superior in case of the treated pigment.

EXAMPLE V Calcium sulphate anhydrite, prepared and calcined as described underExperiment..IVabove, was milled in an edge runner mill with 0.3 per cent diethylaminoethanol, (C2H5) 22N.C2H4.OH,

f followed'by disintegration in a hammer mill.

" The milled, treated and disintegratedcalcium sulphate anhydrite, when usedas anextender in organic coatingv vehicles, and particularly when incorporated in 11% wall paints bodied-with a small amount of water produced coating compositions, which were markedly superior to similar coating compositions formulated with untreated calcium sulphate extender, in respect to consistency, dispersibility, workability, drying and color stability of the dried film, as well as settling characteristics on storage in containers.

. The amine treatment also produced in the coating compositions, excluding the fiat wall paints, an improved gloss and gloss retention of the dried film.

' The following table presents data with respect to the efliciency of certain amino-compounds in lowering the bodying tendency'of composite titanium dioxide-calcium sulphate pigment having a bodying tendency determined in the manner above described of 2400.

From the foregoing it will be seen that when calcium sulphate pigments are treated with amino-compounds according to the present invention there results not only a lowering of the bodying tendency but the pigment is also improved in other respects, particularly, as to mixing properties and dispersibility in various vehicles, drying properties, color stability and gloss retention of surface coating compositions containing the pigment.

From this description of the invention it will be seen that by means of the present invention the bodying tendency of calcium sulphate pigment may be controlled as desired. Pigments prepared according to the invention are particularly adapted for use in surface coating compositions, especially fiat wall paints for interior finishes. They also are excellently adapted for use in inks, paper, rubber, plastics and similar compositions in which such pigments are incorporated.

We claim:

1. Method for lowering the paint bodying tendency of a calcium sulphate pigment which comprises admixing with a calcium sulphate pigment a small amount of an organic aliphatic amine containing at least 2 nitrogen atoms.

2. Method according to claim 1 wherein the amino-compound specified is tetraethylene pentamine.

6. An improved calcium sulphate pigment having reduced paint bodying tendency prepared according to the method of claim 1.

7. Improved pigmentary calcium sulphate having reduced paint bodying tendency prepared according to the method of claim 1.

8. Improved composite titanium dioxide-calcium sulphate having reduced paint bodying tendency pigment prepared according to the method of claim 1.

FRANKLIN L. KINGSBURY. FRANK J. SCHULTZ. 

